Turbomachines, such as gas turbine engines, typically include a fan section, a turbine section, a compressor section, and a combustor section. The fan section drives air along a core flow path into the compressor section. The compressed air is mixed with fuel and combusted in the combustor section. The products of combustion are expanded in the turbine section.
A typical jet engine has two or three spools, or shafts, that transmit torque between the turbine and compressor sections of the engine. Each of these spools is typically supported by two bearings. One bearing, for example, a ball bearing, is arranged at a forward end of the spool and is configured to react to both axial and radial loads. Another bearing, for example, a roller bearing is arranged at the aft end of the spool and is configured to react only to radial loads. This bearing arrangement fully constrains the shaft except for rotation, and axial movement of one free end is permitted to accommodate engine axial growth.
Commercial turbofan engines typically use low pressure compressors coupled to a fan. Advances in coupling the fan to the low pressure compressor have allowed the compressor to operate at higher speeds and to decrease the number of compressor stages required of the compressor. Decreasing the number of stages and increasing the rotational speed of the low pressure compressor causes existing flowpath designs to be non-optimal and may result in decreased performance when the existing flowpath designs are used.